Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be accessed by wireless devices of multiple users sharing the available system resources (e.g., time, frequency, and power). Examples of such wireless communications systems include Code-Division Multiple Access (CDMA) systems, Time-Division Multiple Access (TDMA) systems, Frequency-Division Multiple Access (FDMA) systems, 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) systems, and Orthogonal Frequency-Division Multiple Access (OFDMA) systems. These wireless communication systems generally use different radio access technologies and communication protocols, operate at different frequency bands, provide different quality of service (QoS) and offer different types of services and applications to the system users.
Due to the differences between these systems, wireless devices that were previously designed to operate on one system would not be capable of operating on another. To address this, wireless devices referred to as multimode devices were introduced and rapidly grew in popularity. Multimode devices are capable of operating on multiple heterogeneous wireless communication systems. Multimode devices are generally programmed to search for all available communication systems and connect to the most-preferred one, as specified by the operator or user preference.
Known system reselection techniques have limitations. For example, if the reselection period is too large, the wireless device would spend a longer time camped on the current less-preferred system. This could be detrimental to operator requirements. On the other hand, if reselection is done too often, the device will use a significant amount of time and power in scanning for other systems, which would adversely affect the battery life.
Furthermore, the duration of the scan may also cause problems. During reselection scanning, the wireless device's radio is tuned to frequencies other than the current channel. This means the device spends time not monitoring the paging channel on the current system, which may result in missed pages. Thus, having a long scan may be a disadvantage. In contrast, if the duration is too small, and if the reselection scan list is long enough not to fit in a single reselection instance, the device may never find the better system located at the end of the scan list.
Therefore, it would be desirable to have better reselection approaches.